Electrical charge air compressor provided with an integrated air cooling system

ABSTRACT

The invention relates to a device to compress combustion air, in particular a device to compress combustion air for a combustion engine of a motor vehicle, with a housing ( 12 ), with at least one compressor impeller ( 30 ) arranged in a compression area ( 28 ) of a first housing part ( 14 ), which is arranged in the flow direction between an air inlet ( 24 ) and an air outlet ( 43 ) of the housing ( 12 ), as well as with an electric motor ( 18 ) arranged in a second housing part ( 16 ) of the housing ( 12 ) to operate the compressor impeller ( 30 ). It is proposed in accordance with the invention that a flow channel ( 42 ) running in the circumferential direction of the first housing part ( 12 ) and connecting the compression space ( 28 ) with the air outlet ( 43 ) surrounds the electric motor ( 18 ) at least partially.

PRIOR ART

The invention relates to a device to compress combustion air, inparticular an electrically operated charge-air compressor with thefeatures of the pre-characterizing clause of Claim 1.

Increasing the power density of an internal combustion engine bycompressing the air required for combusting the fuel by means of anexhaust-gas turbocharger is known. In this case, the exhaust-gasturbocharger features a turbine, which is arranged in the exhaust-gasflow of the combustion engine and which drives a compressor arranged inthe charge-air feed of the internal combustion engine.

These types of exhaust-gas turbochargers have the known disadvantage ofdelayed and inadequate response characteristics at low rpms of theinternal combustion engine (“turbocharger gap”).

In order to improve the charge-air feed, especially in the range oflower rpms of the internal combustion engine, supporting the exhaust-gasturbocharger by means of an electric auxiliary drive is known. This canbe achieved, for example, via an electric motor integrated into theexhaust-gas turbocharger. The electric motor then drives the shaft ofthe compressor of the exhaust-gas turbocharger at low rpms of theinternal combustion engine. This kind of hybrid drive of the exhaust-gasturbocharger requires both a high rpm loading capacity of the electricmotor as well as a high electric power requirement because of the highmoment of inertia of the turbine of the exhaust-gas turbocharger that isnecessarily heat-resistant and embodied of steel. In addition, theinstallation volume of such a exhaust-gas turbocharger is increased bythe integration of the additional electric motor.

In order to avoid the disadvantages of the this type of hybrid drive,operating a separate, purely electrically operated auxiliary charger(electric auxiliary compressor) in the charge-air feed of an internalcombustion engine in series with a conventional, turbine-operatedexhaust-gas turbocharger is known from U.S. Pat. No. 6,029,452, forexample. This has the great advantage that the electric auxiliarycompressor that is used separately from the charge-air feed can beoptimized for a short-term use in the lowest rpm range of the internalcombustion engine. Typically, the electric auxiliary compressor isconnected in series with the exhaust-gas turbocharger so that theachievable charge-air pressure is yielded as a product of the individualpressure values.

The short-term, very high-speed operation of the electric auxiliarycompressor produces very high thermal stress to these system components.In addition to passively deriving the excess heat, also cooling theelectric auxiliary compressor itself in operation via the inductedcharge air is also known. For active air cooling, it is proposed in U.S.Pat. No. 5,904,471 that the inducted air flow first be directed alongthe motor housing or directly through the motor housing and then be fedto the compression space of the auxiliary compressor. The arrangement ofthe compressor impeller on the side of the driving motor opposite fromthe induction opening as well as guiding the airflow through the motoritself results in an increased flow resistance for the passivecharge-air compressor. Such a system has the disadvantage of lowerefficiency that can be achieved for the charge-air pressure.

In the range of high rpms of the internal combustion engine, whichsimultaneously leads to a high rpm of the exhaust-gas turbocharger andis therefore also connected with a high throughput of charge air alonedue to the conveyance effect of the exhaust-gas turbocharger, a bypasssolution is used to feed the charge air directly to the compressor ofthe exhaust-gas turbocharger while bypassing the auxiliary compressorthat is now no longer needed. As a result, it is necessary for theelectric auxiliary compressor to have, in its passive operation, thelowest possible flow resistance of the charge air inducted by theexhaust-gas turbocharger.

Integrating a bypass channel in the electric auxiliary compressor isknown from U.S. Pat. No. 5,904,471. A flap valve used in U.S. Pat. No.5,904,471, which diverts the charge-air flow into the bypass channel sothat it is not directed via the compression space and the thereinarranged compressor impeller of the electrically operatedturbo-compressor. This type of flap-controlled bypass solution is notoptimal, however, with respect to the flow-related requirements of theauxiliary compressor and is very costly and expensive for charge-aircompression in terms of the requirements for assembly, size and cost ofthe overall system.

In particular, increased flow resistances are produced in the auxiliarycompressor with a bypass solution in accordance with U.S. Pat. No.5,904,471 since, among other things, corners and edges that produceturbulent flow conditions are present in the flow channel due to theembodied flap valve.

The objective of the invention is further developing an electricauxiliary compressor to the effect that it makes air cooling of itscomponents with the lowest possible flow resistance possible in bothactive as well as passive operation.

The objective on which the invention is based is attained via a deviceto compress combustion air with the features of Claim 1. Advantageousdevelopments and embodiments are yielded from the features listed in thesub-claims.

ADVANTAGES OF THE INVENTION

The electrically driven charge-air compressor in accordance with theinvention having the features of Claim 1 avoids the disadvantagesoccurring in the prior art and makes it possible to operate an electricturbo-compressor in the charge-air feed of an internal combustion enginein series with an exhaust-gas turbocharger for example, whereby theauxiliary compressor in accordance with the invention is air cooled inactive as well as passive operation. Air cooling is made possible in anadvantageous manner while avoiding an increased flow resistance of theelectric auxiliary compressor.

The device to compress combustion air in accordance with the inventionfeatures a housing with a first housing part, in which at least onecompressor impeller is arranged in a compression space of the housing,which is arranged in the flow direction between an air inlet and an airoutlet of the housing. In addition, the housing of the auxiliarycompressor in accordance with the invention features a second housingpart, in which an electric motor is arranged to operate the compressorimpeller. Due to the fact that a flow channel running in thecircumferential direction of the housing and connecting the compressionspace with the air outlet surrounds the electric motor at leastpartially, a thermal coupling is possible between the compressedcharge-air flow and the electric motor driving the compressor.

Advantageous developments and exemplary embodiments of the invention aremade possible by the features contained in the sub-claims.

The flow channel of the compressed charge air is embodied in such a wayin the auxiliary compressor in accordance with the invention that thereis a thermal coupling between the flow channel and the electric motor orbetween the flow channel and the second housing part that accommodatesthe electric motor.

The second housing part is advantageously formed at least partially of aheat conducting material, e.g., a metal.

A compact and very good heat-conducting embodiment of the auxiliarycompressor in accordance with the invention is produced if the flowchannel is essentially embodied in the second housing part itself. Inthe electric auxiliary compressor in accordance with the invention, thespiral-embodied connecting channel between the compression space of thecompressor and the outlet opening of the compressor is “folded down” inthe direction of the driving electric motor as compared to prior artembodiments. The hanging volute (compressor worm), i.e. a volute woundaround the housing of the drive, therefore provides for an optimalcooling of the motor and electronics. Experience has shown that anespecially favorable flow shaping of the air-conducting housing isidentified by a straight, i.e. axial, inlet and a spiral outlet arrangedon the circumference of the housing.

In a particularly advantageous exemplary embodiment of the auxiliarycompressor in accordance with the invention, the flow channel (volute)is a part of the metal housing. The high air mass flow through thevolute both in active as well as passive operation of the auxiliarycompressor provides for optimal cooling of the metal body in which thedriving motor for the compressor is accommodated. In addition to thedriving electric motor, a compartment can also be embodied in the motorhousing, which contains the electronic components of the motor or thecompressor control that are to be cooled.

The motor housing advantageously has a smaller diameter than the insidediameter of the flow channel arranged on the circumference of thecompressor housing. In this way, it is possible to allow the electricmotor or the housing accommodating the electric motor to be enclosed atleast partially in the axial direction without the construction volumeof the compressor in accordance with the invention also being increasedas well.

The very compact construction size of the auxiliary compressor inaccordance with the invention is also the result of the fact that theflow channel is arranged on the high-pressure side of the compressorimpeller. In particular, the flow channel (volute) can be arranged onthe side of the compressor impeller facing away from the air inlet. Thisembodiment of the flow channel allows an effective air cooling of thecompressor housing or the electric motor driving the compressor impellerto be achieved without a special flow diversion being required for thecooling effect. And what is more, the optimized flow guidance in theform of a spiral volute can also be used in an advantageous manner tocool the housing.

In order to keep the flow resistance of the auxiliary compressor inaccordance with the invention as low as possible even the passiveoperating case, i.e. with the electric motor turned off, the compressorin accordance with the invention features a bypass channel, whichconnects the inlet channel of the compressor directly with the flowchannel (volute). Because the flow channel can be connected with theinlet channel of the housing via the bypass channel, theinvention-related shaping of the flow channel also makes a great coolingeffect possible in passive operation. As a result, one and the same flowchannel can be used advantageously in the auxiliary compressor inaccordance with the invention to cool the components both in active aswell as in passive operation. In the passive operating mode, whichrepresents the predominant operating mode of the electric auxiliarycompressor, it has only the task of allowing the airflow to pass throughwith the lowest possible flow resistance. In the process, the componentscan use the passing air to bring itself to the lowest possible operatingtemperature for the next use.

The compressor in accordance with the invention advantageous featuresmeans to close the bypass channel with an activated electric motor. Asimple and reliable manner of closing the bypass channel consists ofusing the swirl of the air flowing radially out of the compressorimpeller to close the bypass channel via, e.g., blades arranged in thediffuser of the compressor. In doing so, the bypass channel is closedboth on its side facing the inlet channel of the compressor as well ason its side facing the flow channel (volute). Closing the flow channelon both sides advantageously permits air turbulence on the inlets of thebypass channel to be realized and therefore increased flow resistance inthe active operation of the compressor.

The device in accordance with the invention also features means, inparticular elastic means, to quickly and reliably open the bypasschannel with a deactivated electric motor. Because of the large flowcross-section of the bypass channel, the auxiliary compressor inaccordance with the invention constitutes only a very low flowresistance in a passive operating case. This makes favorable efficiencyof the overall system of the charge-air feed or the combustion enginepossible also in a passive operating case of the auxiliary compressor.

The claimed device to compress combustion air makes possible anelectrically driven auxiliary compressor for the charge air of a motorvehicle, which makes efficient cooling possible, in particular coolingvia the inducted charge air, without producing increased air resistance.Due to the fact that the air cooling is possible both in the active aswell as passive operation of the electric charge-air compressor and ittakes place advantageously through the same flow channel, the thermalstress can be kept low for such an electrical auxiliary compressor thatis operated at high speed.

Additional advantages of the device in accordance with the invention canbe found in the following drawings as well as in the associateddescription of an exemplary embodiment of a device in accordance withthe invention to compress combustion air.

DRAWINGS

Two exemplary embodiments of a device to compress combustion air aredepicted in the drawings, and these exemplary embodiments are supposedto be explained in more detail in the following description. The figuresin the drawings, the description thereof, as well as the claims aimed atthis, contain numerous features in combination. A person skilled in theart will also observe these features individually and combine them intoadditional, meaningful combinations.

The drawings show:

FIG. 1 A schematic representation of a cross-section through anelectrically operated charge-air compressor in accordance with theinvention.

FIG. 2 A cross-section through an alternative embodiment of a charge-aircompressor in accordance with the invention with a closed bypasschannel.

FIG. 3 A cross-section through the charge-air compressor in accordancewith FIG. 2 with an opened bypass channel.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

FIG. 1 shows a schematic representation of a first exemplary embodimentof the device in accordance with the invention to compress combustionair. The compressor 10 features a housing 12, which is embodied asseveral pieces in the exemplary embodiment in FIG. 1. The housing of thecompressor essentially includes a first housing part 14 for the actualcompressor head 22 of the device (also called compressor part of thedevice in the following) and a second housing part 16, which surroundsthe driving means for the compressor and, in the exemplary embodiment inFIG. 1, essentially includes an electric motor 18 driving the compressoralong with associated electronic components. The second housing part 16of the compressor in accordance with the exemplary embodiment in FIG. 1is in itself constructed of three parts for manufacturing-relatedreasons. The housing part 16 includes the actual motor housing 17 of thedriving electric motor 18, which is embodied as a pole pot or as a tube,a diffuser ring 19, which is arranged in the axial direction between thecompressor head 22 and the motor housing 17 and a third housing part 15,which contains a compartment 52 for electronic components to trigger thecompressor and a part of the flow channel of the compressor.

In addition the housing 12 features a base 20 closing the one housingpart 16, which enables easy access to the motor part of the device andin addition also supports a bearing of the drive shaft of the compressorimpeller.

The compressor head 22 of the compressor 10 is embodied as a radialcompressor with axial induction. The first housing part 14 for thecompressor head 22 has a bell-shaped or funnel-shaped design with aninlet channel 24, which is formed by an inlet connection piece 26 of thefirst housing part 14.

A compression space 28, in which a compressor impeller 30 is arranged,is embodied in the first housing part 14. The compressor impeller 30 isarranged concentrically to the inlet channel 24 of the first housingpart 14 of the compressor 10. The compressor impeller 30 features a flatunderside 32, which is facing the second housing part 16 of thecompressor 10 and the diffuser ring 19 in particular. The upper side ofthe compressor impeller facing away from underside 32 of the compressorimpeller 30 is provided in a manner that is known per se with compressorstructures 34 in the form of three dimensionally embodied blades. Afirst flow channel 36 extends from the inlet channel 24 of thecompressor 10 in the axial direction of the compressor into thecompression space 28. The charge air inducted through the first flowchannel 36 when the compressor is in operation is accelerated via thecompressor impeller 30 and pressed radially to the outside. On itsradial ends 38, the compression space 28 turns into a radial diffuser40. The radial diffuser 40 in turn terminates in a flow channel 42,which, as a worm, widens continuously at the circumference of thehousing 12 and acts as a collector for the compressed charge air. At thepoint at which the spiral flow channel 42 (volute) hits its beginning inthe circumferential direction of the compressor, the flow channel 42moves tangentially away from the housing 12 of the compressor. Theradial diffuser 40 also ends tangentially in the flow channel 42. Thediffuser ring 19, which therefore conveys the air from the compressorimpeller into the flow channel 42 on its upper side facing thecompressor impeller 30, is simultaneously cooled in the process by thisair. In this connection, it forms, together with the underside of acontrol hood 60, a ring diffuser for a bypass channel of the compressorand this ring diffuser delays the airflow and therefore builds uppressure. Beyond this, the diffuser ring 19 serves at the same time asan end shield for the drive shaft of the electric motor 18.

In the exemplary embodiment of the compressor in accordance with theinvention shown in FIG. 1, the part of the flow channel 42 (shown in theupper area of the drawing, i.e. facing the compressor head 22) is formedby the first housing part 14 of the compressor and the diffuser ring 19of the housing 16 so that the diffuser ring 19 can also be cooled by theair in the flow channel 42.

In the device in accordance with the invention, the flow channel 42(volute) is folded down in the axial direction and therefore aligned inthe direction of the second housing part 16 of the electric motor 18.(Normally, in the case of corresponding prior art compressors, thevolute is adjacent above a radial diffuser, but pointed towards theinduction side.) The flow channel 42 in accordance with the exemplaryembodiment in FIG. 1 is embodied in the second housing part 16 of thecompressor 10, which is adjacent in the axial direction to thecompressor impeller. The second housing part 16, which encloses theelectric motor 18 driving the compressor, consists advantageously of agood heat-conducting material. In particular, this housing can bemanufactured of a metal, e.g., aluminum. This housing part includes theflow channel 42 and a support 52 for electronic components 54(electronics compartment) of the drive system. In the process, the airflowing by in the flow channel 42 cools, for one, the electric motor 18via the diffuser ring 19 and secondly also the electronic components 54in the electronics compartment 52.

The flow channel 42 of the compressor can be embodied in variouscross-sectional shapes. A cross-section that is approximately ellipticalis advantageous. There is only a small difference in the sizes of thesemiaxis of the elliptical cross-sectional shape in the exemplaryembodiment depicted in FIG. 1. The ellipticity can be more pronounced inother exemplary embodiments.

Thus, it is also possible for example to embody and arranged the flowchannel 42 in such a way that the large semiaxis of the ellipseinscribing the channel runs parallel to the drive shaft of thecompressor. It is possible in this way to cool the motor housing 17 overa large surface via the airflow of the flow channel 42. However, thecompressor in accordance with the invention is not limited to the use ofan elliptical cross-sectional profile for the flow channel 42. Circularor other cross-sectional shapes are also possible.

The driving motor 18, which features a stator 44 as well as a rotor 48connected to a drive shaft 46, is embodied in such a way that the motorhas a smaller diameter than the inside diameter of the flow channel 42.In this way, it is possible for the flow channel 42 that is folded downin the direction of the electric motor 18 and running in thecircumferential direction of the housing 12 to enclose the electricmotor completely in the circumferential direction and to surround it atleast partially in the axial direction.

The lower part of the flow channel 42 facing the electric motor 18 isworked out in the housing part 15 or 19. For manufacturing-relatedreasons, the housing 16 is embodied of several parts. The housing part15 also includes the support 52 for the electronic components for themotor triggering. The high air mass flow in the flow channel 42 providesfor optimal cooling of the metal body 50 of the housing part 15. Thegood thermal conductivity of the metal therefore provides for goodcooling of the electronics compartment 52, which is embodied in thesecond housing part 15. In addition, the driving motor 18 with itshousing 17, which is enclosed in the radial direction by the housingpart 15, is also cooled by the metal body 50.

Electronic components 54 of the power electronics are attachedadvantageously to trigger the electric motor 18 or to operate thecompressor 10 in thermal contact with the metal body 50. In this case,the electronic components and particularly the power semiconductorsgenerating high power dissipation can be fastened directly to thehousing part 15 with or even without heat conducting means. In this way,it possible to realize good thermal transmission, i.e. a high heat flowfrom the electronic components 54 into the air that is located in theflow channel 42. The electronics compartment 52 has a cover 56, which ifneed be can provide for corresponding openings in its outer side 57 foradditional heat exchange with the environment. In addition, as alreadydescribed, the housing part 17 of the electric motor is strongly coupledthermally to the diffuser ring 19 and the housing part 15 so that theheat produced by the motor can be dissipated well in this way.

FIGS. 2 and 3 show a compressor 11 that has only been slightly modifiedwith respect to the driving motor. When the compressor 10 or 11 is inactive operation, the electric motor 18 drives the compressor impeller30 in the compression space 28 via the drive shaft 46. In the exemplaryembodiment in FIGS. 2 and 2, the housing 16 of the compressor 11 isembodied as a single piece. Even though this has manufacturing-relateddisadvantages, it provides for optimal cooling of both the motor 18 aswell as the electronic components 54 via the air of the flow channel 42.

The adaptation to various mass flows in the active or passive state ofthe compressor 10 or 11 is accomplished by means of a control hood 60,which is arranged in a bell-shaped manner in the first housing part 14between the inlet connection piece 26 and the compression space 28 ofthe compressor. A bypass channel 62 branches off of the inlet connectionpiece 26 in an almost tangential direction and this bypass channel makesa connection possible between the inlet channel 24 and the flow channel42. The bypass channel 62 discharges in this case into the outletcircumference of the radial diffuser 40, which at this point turnsdirectly into the flow channel 42.

Blades 64, which are in mechanical working connection with the controlhood 60, are arranged in the radial diffuser 40. When the compressor 10or is in an active state, the swirl of the compressed air flowingradially from the compressor impeller 30 into the radial diffuser 40drives the control hood 60 in the direction of rotation of thecompressor impeller by means of the blades 64 in the diffuser. Thecontrol hood 60 is positioned in the housing 14 in such a way that itrotates around a defined angle via the air swirl and in doing so closesthe bypass channel 62 due to the twisting of the windows 66 or othercorresponding closing elements 68. In this case, the inductedcompression air reaches from the inlet connection piece 26 directly intothe compression space 28, in that it is accelerated via the compressorimpeller 30 and thereby compressed. The air is transmitted via the flowchannel 42 in the direction of the outlet channel 43. In thisconnection, in the case of the compressor 10 or 11 in accordance withthe invention, both sides of the bypass channel 62, i.e. both thebeginning of the bypass channel 62 facing the inlet channel 24 as wellas the end of the bypass channel 62 facing the radial diffuser 40, areclosed via the closing elements 68 or by twisting the windows 66 in thecontrol hood 60. It is possible in this way to avoid the formation ofwhirling that could form, e.g. at the opening of the bypass channel tothe radial diffuser. Such formation of whirling represents a high flowresistance and would have a disadvantageous effect on the favorable andtherefore low-loss flow that is striven for.

The control hood 60 is positioned in the housing 14 in such a way thatit rotates around a defined angle via the air swirl acting upon theblades 64 and in doing so tenses a spring device 70 situated between thecontrol hood 60 and housing 14.

If the electric drive 18 of the compressor 10 or 11 is turned off, thespring device 70 provides for a restoring moment, which rotates thecontrol hood 60 back into its initial position (shown in FIG. 3) andthereby removes the closing elements 68 in front of the ends of thebypass channel 62 and opens the bypass channel.

FIG. 3 shows the device in accordance with the invention with an openedbypass channel 62. The compressor air, which is inducted through theconnected-in-series exhaust-gas turbocharger for example, reaches thecontrol hood 60 of the compressor in accordance with the invention viathe inlet channel 24 and the first flow channel 36 and from there viathe window elements 66 into the now opened bypass channel 62. Because ofthe large flow cross-section in the inlet channel 24, the window 66 aswell as in the bypass channel 62, the air flowing through the passiveauxiliary compressor experiences only a low flow resistance and in turnreaches the flow channel 42 almost unimpeded and from there the outlet43 of the compressor 10 or 11. On its way through the flow channel 42,the inducted air enables efficient cooling in particular of the secondhousing part 16 with the driving motor 18 that is arranged therein. Thecompressor 10 or 11 can use the passing air in this passive operatingmode to bring itself to the lowest possible operating temperature forthe next use.

With the described device, it is advantageously possible to realizecooling of both the driving electric motor as well as the associatedelectronics of an electrically operated auxiliary compressor with theaid of the induction air without having to do without the flow-relatedoptimal shaping of the flow of the inducted charge air in the process.Favorable and therefore low-loss flows can be embodied in both operatingmodes with this device, which in any case produces a more favorableefficiency of the combustion engine with associated charge-air feed. Dueto the arrangement of a flow-related optimal flow channel in accordancewith the invention, it is possible to realize optimal cooling of theelectronic components of the device while maintaining the largestpossible flow cross-sections, even when using a bypass channel inpassive operation of the compressor in accordance with the invention.

The electrically operated charge-air compressor in accordance with theinvention is not restricted to the exemplary embodiment presented in thedrawings. In particular, the device is not restricted to the use of onlya single compressor impeller.

The charger-air compressor in accordance with the invention is notrestricted to the use of a control hood for the integrated bypasschannel.

1. Device to compress combustion air, in particular a device to compresscombustion air for a combustion engine of a motor vehicle, with ahousing (12), with at least one compressor impeller (30) arranged in acompression area (28) of a first housing part (14), which is arranged inthe flow direction between an air inlet (24) and an air outlet (43) ofthe housing (12), as well as with an electric motor (18) arranged in asecond housing part (16) of the housing (12) to operate the compressorimpeller (30), characterized in that a flow channel (42) running in thecircumferential direction of the first housing part (12) and connectingthe compression space (28) with the air outlet (43) surrounds theelectric motor (18) at least partially in the axial direction.
 2. Deviceaccording to claim 1, characterized in that the flow channel (42) isconnected with the electric motor (18) and/or the second housing part(16).
 3. Device according to claim 1, characterized in that theelectronic components (54), in particular the electronic components ofthe motor electronics of the driving electric motor (18) are integratedin such a way in the second housing part (16) that the electronics (54)are cooled predominantly via the flow channel (42).
 4. Device accordingto claim 2, characterized in that the second housing part (16) iscomprised at least partially of a heat conducting material.
 5. Deviceaccording to claim 4, characterized in that the second housing part (16)features a diffuser ring (19), which forms a portion of the limitationof the flow channel (42) and is thermally coupled to the electric motor(18).
 6. Device according to claim 2, characterized in that the flowchannel (42) is essentially embodied in the second housing part (16). 7.Device according to claim 6, characterized in that the flow channel (42)is embodied as a single piece with the second housing part.
 8. Deviceaccording to claim 1, characterized in that the flow channel (42) isarranged at the high-pressure side of the compressor impeller (30). 9.Device according to claim 8, characterized in that the flow channel (42)is arranged on the side of the compressor impeller (30) facing away fromthe air inlet (24).
 10. Device according to claim 1, characterized inthat the flow channel (42) features a cross-section that widens in thecircumferential direction of the housing (12).
 11. Device according toclaim 10, characterized in that the flow channel (42) features anessentially elliptical cross-section, whereby the large semiaxis of theellipse runs essentially parallel to the drive shaft (46) of theelectric motor (18).
 12. Device according to claim 1, characterized inthat the flow channel (42) can be connected with the air inlet (24) ofthe housing (12) via a bypass channel (62) bypassing the compressorimpeller (30).
 13. Device according to claim 12, characterized in thatmeans (64, 68) are provided to close the bypass channel (62) with anactivated electric motor (18).
 14. Device according to claim 13,characterized in that the means (64, 68) are self-setting.
 15. Deviceaccording to claim 13, characterized in that the means (64, 68) are airdriven.
 16. Device according to claim 12, characterized in that themeans (70), in particular elastic means, are provided to open the bypasschannel (62) with a deactivated electric motor (18).
 17. Deviceaccording to claim 2, characterized in that the electronic components(54), in particular the electronic components of the motor electronicsof the driving electric motor (18) are integrated in such a way in thesecond housing part (16) that the electronics (54) are cooledpredominantly via the flow channel (42).
 18. Device according to claim3, characterized in that the second housing part (16) is comprised atleast partially of a heat conducting material.
 19. Device according toclaim 14, characterized in that the means (64, 68) are air driven. 20.Device according to claim 15, characterized in that the means (70), inparticular elastic means, are provided to open the bypass channel (62)with a deactivated electric motor (18).